Ideally, you should have reset the Apple TV device to erase any customization, including your account.
Reset or restore your Apple TV to its factory settings - Apple Support
Now you have to hope that the new user will do this as a first step. If you have a means to contact them, then ask them to do this reset.
What you can do now, is disassociate your account from that device (“Remove device from account”). After that, and once someone will try to access anything specific to your account, then they will find that they have to sign in again, which won’t work (unless they know the password to your Apple ID – which they shouldn’t). Then the best way forward for the new user, is to reset as mentioned above.
Check your Apple ID device list to find where you're signed in - Apple Support
iPhone: Settings﹥[you/your Apple ID]﹥scroll down to devices﹥Apple TV 4K﹥Remove from Account.
Apple TV services on your other devices will remain as they were, as those are tied to your personal Apple ID account.